Introduction: Poor Man's CNC Edge Finder

Aluminum foil tape offers a very simple, precise and cheap way to zero almost any workpiece.

Things you need:

  • Aluminum foil tape - it can be found at most hardware stores.
  • One or two alligator clips.
  • A 100nF ceramic capacitor (optional but recommended)
  • A CNC controller with sensor assisted edge finding capabilities like Estlcam

Step 1: How It Works

How it works:

  • The aluminum tape and tool act as switch. Once the tool touches the tape the circuit is completed and the probe input of the CNC controller triggers.
  • The aluminum tape is connected to the probe input using an alligator clip.
    (Pin D6 for Estlcam / A5 for GRBL)
  • The tool is connected to GND
    • I've connected GND to the spindle housing as it is conductive all the way through to the tool.
      (Check this first - not all spindle housings are conductive and connected to the tool.)
    • This way the GND connection can stay permanently and you can even touch off with the spindle running.
  • Add a 100nF ceramic capacitor between probe input and GND close to the controller - this suppresses interferences which may trigger the input unintentionally.

Step 2: Prepare the Tape

Prepare the tape:

  • Prefer tape with liner - it is easier to work with.
  • Cut a short length of tape from the roll and turn it over.
  • Fold the liner back lengthwise to expose the upper half of the glued aluminum foil.
  • Then fold about 5mm (1/4") of the tape itself down and put the liner back.
  • Finally cut the tape into short stripes.


  • Ready to use strips.
  • Liner can be removed easily.
  • Folded back part of the tape does not keep sticking to the alligator clip.

Step 3: Final Thoughts

You'll find most information in the video at the beginning - so just a few final thoughts:

  • The tape can be reused several times. The wrinkles add some thickness and therefore error but for most applications this should be insignificant (I've measured a difference of 0.02mm / 0.0008" between new and badly wrinkled tape)
  • This also works for conductive workpieces with a small modification, even if the machine bed and workpiece is connected to GND. Just put regular tape below the aluminum tape to add an isolation layer.
  • Be careful with coated tools. Some coatings are non-conductive so the circuit will not close -> risk of breaking the tool. If in doubt check the tool with a multimeter first.
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